Sensors for detection of biological substances based on nanoscale field-effect transistors, such as for example silicon nanowire FETs and carbon nanotubes with properly functionalized surfaces, have enormous potential for very sensitive detection of minute (down to femtomolar) concentrations of biomolecules such as proteins and DNA. In addition, when proper interface layers are applied through functionalization of the surface in contact with the active substance, these devices are potentially interesting for sensing gasses as well.
In all applications where the nanoscale field-effect transistor is used there is a strong desire for sensing multiple target molecules simultaneously. In a liquid or gas environment, the use of a reference transistor is of crucial and critical importance in order to compensate for time related drift.
For many applications of gas sensors, such as indoor air quality (IAQ) management, HVAC, asthma, cardiovascular diagnosis, and greenhouse control, a high sensitivity combined with a wide dynamic range is required. Mass spectrometry is the standard method for gas detection. This technique is sensitive, selective and has a wide dynamic range, but is also costly and sizable. Alternatively, optical detection, more specifically absorption spectroscopy in the infra red (IR), is being used as a gas sensor. This technique is sensitive and selective, but one module can only detect one type of molecule and the measurement equipment is costly and sizable. Electrochemical detection can also be used but does not provide the proper sensitivity or the selectivity.
US2010/0243990 discloses a nanowire-based sensor device for detecting bio-molecules. The devices are based on a silicon nanowire field-effect transistor, where the nanowire can be either n-type or p-type impurity doped. The surface of the nanowire is functionalized by molecules that specifically couple to their targeted counterparts. The charges on the target molecules affect the conductivity of the nanowire channel like a gate-electrode.